Prior to the present invention, there have been fertilizers specifically designed/formulated for the nutritional-treatment of iron-deficient plants by foliar treatment with solubilized-iron ethylenediamine tetraacetic acid(EDTA), a sulfate foliar chelated-iron aqueous solution of which a typical commercially-available fertilizer is Sequestrene 138 (Ciba-Geigy trademark). Greenol(Chevron Chem.) analyzes at 6.13% Fe(iron), 0.13% Cu(copper), 0.10% Zn(zinc) and 3.64% S(sulfur). Citric acid alone has likewise been recognized in prior art to be a sequestering agent. While iron must be made soluble in order to be assimilated by plants, whether by roots or by foliage to which it has been applied, virtually all iron present must be present in some special form or complex in order to not destroy the foliage by foliage phototoxicity, burn or the like. However, not every complex of iron renders it suitable for use as a foliar spay application, for example phosphate-containing iron-supplementing fertilizer interferes with foliage iron-assimilation by both physical and physio-chemical phenomenon, forming amorphous film on foliage to which applied, blocking leaf membranes and interfering with iron transport within the leaf and plant to the extent that iron is not blocked at the leaf pores. As well, phytotoxicity to the foliage is significantly greater and detrimental when a phosphate is applied thereto, as compared to other chelated iron-complexes. Accordingly, for example, the polyphosphate complex of Parham, Jr. U.S. Pat. No. 3,798,020 is totally unsuitable for use in foliar-spray treatment of iron-deficient plants, the Parham, Jr. fertilizer composition being directed exclusively to soil application, as opposed to foliar application.
More particularly, as to the above-noted Parham, Jr. patent, Mr. Parham has himself acknowledged the Parham patent's mention in column 1, lines 54-61 that foliar application of ammonium polyphosphate fertilizer (foliar application) solution incorporating amounts of one or more of the micronutrients copper, zinc, molybdenum or iron in the form of their sulfate salts as disclosed in U.S. Pat. No. 3,558,300, was intended to point-out solely that such polyphosphates incorporating such micronutrients was already known. Mr. Parham points out that the sole practical utility for a fertilizer of the type disclosed as the invention of his above-noted patent, is the utility as a soil-applied fertilizer for uptake by plant root systems, in so far as his knowledge and contemplation set-forth in that patent. Mr. Parham further states that there can be no implication from the disclosure of his patent, that use of such a composition would have adequate adsorption by the plant foliage, as is documented by "A Decade of Synthetic Chelating Agents in Inorganic Plant Nutrition", Arthur Wallace, Editor (Professor of Plant Nutrition; University of California, Los Angeles) published July 1962 by Arthur Wallace, 2278 Parnell Avenue, Los Angeles, Calif., stating on page 135 thereof "High phosphorous levels and calcium levels also decrease translocation of foliar-applied iron."
Accordingly, while phosphates may be marginally acceptable for some types of fertilizers, phosphates are detrimental and clearly unsuitable and undesirable as potential component(s) of an iron-containing fertilizer formulated and/or designed specifically to obviate iron deficiency of plants growing in geographical areas deficient in iron nutrient as a part of the natural soil. The presence of a phosphate, as above-stated and documented, would defeat substantially the purpose and possibility of success of any foliar composition containing such phosphate and the utility thereof as an iron-source foliar fertilizer. This is in contrast to fully acceptable use of phosphates for fertilizers of a type not directed to supplementing iron-nutrient in iron-deficient plant, although as noted the amorphous coating resulting from the application of a phosphate to foliage interferes with other nutrients absorption through the phosphate-blocked leaf membranes.
It will thus also be now appreciated and recognized that a specialized fertilizer such as for example the above-noted chelated-iron fertilizers, do not contain ingredients heretofore that would have been a part of some fertilizers not concerned with iron deficiency of plants. Both the invention of the above-noted Parham, Jr. patent, as to its illustrative examples as well as the control-example, that include nitrogen, in fact include such nitrogen-providing ingredient in that Parham, Jr. patent because as Parham, Jr. himself acknowledges his invention of that patent has its practical utiliity as a soil-applied fertilizer, as noted above.
The invention however pertains to also soils having iron present therein, but because of the great insolubility of iron many plants are found to be deficient in iron and in need of the special iron-providing fertilizer providing the iron in an improved form in which it may be better assimilated by the plants.
As noted-above, various iron chelates such as the chelate of ethylenediamine tetraacetic acid (EDTA) have been used to obviate the problems of iron-deficient plants resulting from the insolubility of iron when not chelated. The chelates are complexes of the metal with certain chelating agents which have two or more sites in their molecules for bonding with the metal and which are capable of forming a closed ring with the metal. In this form, the metals are stabilized and most of the solubility problems are obviated. These chelating agents, however, are relatively complex compounds which are too expensive for large scale agronomical use. In addition, many of the chelates are very stable compounds and the chelate structure hinders the utilization of the metal by the plant after its assimilation. Finally, iron complexes of organic ligands and iron salts when used in foliar sprays often cause undesirable objectionable spotting of foliage or crop.
U.S. Pat. Nos. 3,679,377 and 3,753,675 propose solutions to the above problem by utilizing iron for a soil-applied fertilizer, in aqueous solution as the ammonium, alkali metal or alkaline earth metal salt of an ion comprising a complex of trivalent iron, sulfate and hydroxo ligands with a pH of about 1 to about 3, and a sulfate to elemental iron ratio from about 0.25 to about 1.1. In U.S. Pat. No. 3,753,675 a similar complex is described as prepared by admixing an iron source with an aqueous solution of ammonium nitrate having a pH of 1 to about 3 and exposing the mixture to autooxidation conditions comprising temperature and time sufficient to cause evolution of nitrogenous gases from the mixture and form an aqueous solution having a red coloration Such fertilizer solutions have drawbacks of being corrosive to common steel and probably phytotoxic if applied as foliar spray to relieve an iron deficiency.